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用醋酸盐和丁酸盐进行产电的单室微生物燃料电池(英文)

Environ.Sci.Technol.2005,39,658-

用醋酸盐和丁酸盐进行产电的单室微生物燃料电池(英文)

662

ProductionofElectricityfromAcetateorButyrateUsinga

Single-ChamberMicrobialFuelCell

HONGLIU, SHAOANCHENG, ANDBRUCEE.LOGAN*, ,

DepartmentofCivilandEnvironmentalEngineering,andThePennStateHydrogenEnergy(H2E)Center,ThePennsylvaniaStateUniversity,UniversityPark,Pennsylvania16802

Hydrogencanberecoveredbyfermentationoforganicmaterialrichincarbohydrates,butmuchoftheorganicmatterremainsintheformofacetateandbutyrate.Analternativetomethaneproductionfromthisorganicmatteristhedirectgenerationofelectricityinamicrobialfuelcell(MFC).Electricitygenerationusingasingle-chamberedMFCwasexaminedusingacetateorbutyrate.Power

generatedwithacetate(800mg/L)(506mW/m2or12.7mW/L)wasupto66%higherthanthatfedwithbutyrate

(1000mg/L)(305mW/m2or7.6mW/L),demonstratingthatacetateisapreferredaqueoussubstrateforelectricitygenerationinMFCs.Poweroutputasafunctionofsubstrateconcentrationwaswelldescribedbysaturationkinetics,althoughmaximumpowerdensitiesvariedwiththecircuitload.Maximumpowerdensitiesandhalf-saturation

constantswerePmax)661mW/m2andKs)141mg/Lforacetate(218 )andPmax)349mW/m2andKs)93

mg/Lforbutyrate(1000 ).Similaropencircuitpotentialswereobtainedinusingacetate(798mV)orbutyrate(795mV).Currentdensitiesmeasuredforstablepoweroutputwerehigherforacetate(2.2A/m2)thanthosemeasuredinMFCsusingbutyrate(0.77A/m2).Cyclicvoltammogramssuggestedthatthemainmechanismofpowerproductioninthesebatchtestswasbydirecttransferofelectronstotheelectrodebybacteriagrowingontheelectrodeandnotbybacteria-producedmediators.Coulombicefficienciesandoverallenergyrecoverywere10-31and3-7%foracetateand8-15and2-5%forbutyrate,indicating

substantialelectronandenergylossestoprocessesotherthanelectricitygeneration.Theseresultsdemonstratethatelectricitygenerationispossiblefromsolublefermentationendproductssuchasacetateandbutyrate,butenergyrecoveriesshouldbeincreasedtoimprovetheoverallprocessperformance.

Introduction

Harvestingproductsfromwastewaterinordertomaketheprocessmoreeconomicalandsustainableisthenextfrontierinwastewatertreatment(1,2).Hydrogenproductionfromwastewaterbybiologicalfermentationhasdrawnmuchattentionasamethodofproducingavaluableproductduringtreatmentofwastewaterscontaininghighconcentrationsof

*Correspondingauthorphone:814-863-7908;fax:814-863-7304;e-mail:[email protected]

DepartmentofCivilandEnvironmentalEngineering. ThePennStateHydrogenEnergy(HE)Center.2

658

9

carbohydrates(3-7).Onemoleofglucosecantheoretically

beconvertedinto12molofhydrogen,butthemaximumyieldviaknownfermentationroutesisonly4molofhydrogenwhenacetateisthesolebyproduct.Whilethemaximumefficiencyofhydrogenproductionistherefore33%,typicallyonly15%oftheenergyisrecoveredashydrogen(2,8)withtheremainderoftheorganicmatterpresentasfattyacidsandalcohols.

Toimprovetheeconomicsofhydrogenproductionfromwastewater,additionalprocessesareneededtorecoverytheremainingenergy.Oneapproachistolinkhydrogenpro-ductionwithmethaneproductionbyusingatwo-stageprocess(2).Althoughtwo-stageanaerobictreatmentshavebeenusedtomakemethane,ithasnotyetbeenprovenoutsideofthelaboratorythathydrogencanberecoveredathighconcentrationsfromthefirststageusingactualwaste-waters.Asecondapproachistousephototrophicbacteriatorecoveradditionalhydrogenfromthebyproductsofhydrogenfermentation(9,10).Althoughsolarenergyisfree,theavailabilityofsufficientlandareaandtheinstabilityofsufficientsolarenergyattheplantwouldmakesuchaprocessdifficultforwastewatertreatmentapplications.Athirdapproachistorecovertheremainingenergydirectlyaselectricityinamicrobialfuelcell(MFC).WhileelectricityproductionhasbeenshowninMFCsusingglucoseoracetate,muchremainstobedoneinordertousethistechnologyforwastewatertreatment.

Bacteriapresentinwastewater,anaerobicreactorsludges,andmarinesedimentshavebeenshowntoproduceelectricityinaMFC(11-14).Bacteriathathavebeenidentifiedtobecapableofmakingelectricityinfuelcells,mostofwhicharemetal-reducingbacteria,includeGeobactersulfurreducens(15,16),Geobactermetallireducens(13,16),Shewanellaputrefaciens(17,18),Clostridiumbutyricum(19),Rhodoferaxferrireducens(20),andAeromonashydrophila(15).IthasalsobeenrecentlyshownthatelectricitygenerationinanMFCresultedinlargepartfromtheproductionofmediators,orelectronshuttles,byamicrobialcommunityconsistingofprimarilythreebacteria:Alcaligenesfaecalis,Enterococcusfaecium,andPseudomonasaeruginosa(12).

ManyMFCscontaintwochambers(16-18,20).Onechambercontainselectrochemicallyactivebacteriagrowingunderanaerobicconditionsthatgrowasabiofilmattachedtotheanode.Theotherchamberiskeptaerobicbyspargingwaterwithairandcontainsthecathode.Thetwochambersaretypicallyseparatedbyaprotonexchangemembrane(PEM),whichallowsthetransferofprotonsfromtheanodetocathodechamberandthathelpstophysicallyblockoxygendiffusionintotheanodechamber.Recently,single-chamberMFCshavebeendevelopedthatuseacathodeexposeddirectlytoairinsteadofair-spargedwater(11,21,22).Thereareseveraladvantagesofusingasingle-chamberMFCversusatwo-chamberedsystem:increasedmasstransfertothecathode;decreasedoperatingcosts,becauseitisnotneces-sarytospargethewater;anoveralldecreaseinreactorvolume;andasimplifieddesign.Poweroutputcanfurtherbeincreasedinasingle-chamberMFCbyremovingthePEM(11).AlthoughthereisincreasedoxygendiffusionintotheanodechamberintheabsenceofthePEM,theformationofanaerobicbiofilmonthecathodeinnersurface(facingtheanode)removesanyoxygenthatdiffusesintothechamber,preventingthelossofanaerobicconditionsintheanodechamber.ThelackofaPEMalsosubstantiallydecreasesthecostofthematerialsneededtomakeaMFC.

Theprimaryfermentationendproductsduringbiohy-drogenproductionareaceticandbutyricacids.Thus,tolink

10.1021/es048927cCCC:$30.25

©2005AmericanChemicalSociety

PublishedonWeb12/03/2004

ENVIRONMENTALSCIENCE&TECHNOLOGY/VOL.39,NO.2,2005

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